In order to increase the travel stability of automobiles when they turn or travel in a straight line, the following automobiles are starting to be practically used: automobiles including a mechanism for steering the rear wheels in addition to a mechanism for steering the front wheels, or automobiles including a mechanism for changing the toe angles of the rear wheels in accordance with their travel state.
Japanese Unexamined Patent Application Publication No. 2009-173192 discloses a rear wheel steering device for steering rear wheels in accordance with the steering angles of front wheels when a driver steers a steering wheel. This rear wheel steering device includes linear motion actuators provided to the right and left rear wheels, respectively. By the respective linear motion actuators, it is possible to steer the right rear wheel and the left rear wheel independently of each other. This rear wheel steering device can steer the rear wheels in the same direction as or in the direction opposite to the steering angles of the front wheels so as to increase the travel stability of the vehicle when the vehicle turns, or can adjust their toe angles by steering the right and left rear wheels so as to increase the travel stability of the vehicle when the vehicle travels in a straight line.
Japanese Unexamined Patent Application Publication No. 2013-159131 discloses a rear wheel steering device for steering right and left rear wheels together. This rear wheel steering device includes a steering housing fixed to the vehicle, a single, rear wheel steering shaft axially movably supported by the steering housing, a pair of tie rods coupled to the respective ends of the single, rear wheel steering shaft, and knuckle arms coupled to the respective tie rods. By axially moving the single, rear wheel steering shaft, this rear wheel steering device can change the respective steering angles of the right and left rear wheels such that the rear wheels are steered in the same direction as or in the direction opposite to the steering angles of front wheels.
In the rear wheel steering device of Japanese Unexamined Patent Application Publication No. 2009-173192, the linear motion actuators configured to steer the right and left rear wheels, respectively, are mounted below springs of respective suspensions (i.e., not mounted to the side of the vehicle body supported through the suspensions, but mounted to the sides of the wheels supporting the vehicle body through the respective suspensions). Therefore, the weight of the rear wheel steering device is added to unsprung weight, so that a driver might not be able to enjoy a comfortable ride in the vehicle.
In the rear wheel steering device of Japanese Unexamined Patent Application Publication No. 2013-159131, since the steering housing is fixed to the side of the vehicle body, the weight of the rear wheel steering device is not added to unsprung weight. However, this rear wheel steering device cannot steer the right and left rear wheels independently of each other for “toe-in”, “toe-out”, etc.